David Bowie’s duet with Bing Crosby on the entertainer’s 1977 Christmas television special left an indelible impression on Crosby’s teenage children.

Harry, Mary and Nathaniel Crosby were on set when Bowie arrived to tape his appearance. The mash-up between the cardigan-clad singer known for “White Christmas” and the glam rocker who was in his Ziggy Stardust phase required some last-minute reworking of “The Little Drummer Boy.”

The result was a new melody and lyrics called “Peace on Earth.” The duet remains a holiday staple and a curiosity. Bowie was 30 and Crosby was 73 at the time. Crosby died of a heart attack a month after the taping in September 1977.

“The doors opened and David walked in with his wife. They were both wearing full-length mink coats, they have matching full makeup and their hair was bright red,” she told the summer TV critics’ tour Wednesday. “We were thinking, ‘Oh my god.'”

Nathaniel Crosby added, “It almost didn’t happen. I think the producers told him to take the lipstick off and take the earring out. It was just incredible to see the contrast.”

Watching in the wings, the Crosby kids noticed a transformation.

“They sat at the piano and David was a little nervous,” Mary Crosby recalled. “Dad realized David was this amazing musician, and David realized Dad was an amazing musician. You could see them both collectively relax and then magic was made.”

The Crosby siblings — now all in their 50s — and their 80-year-old mother, Kathryn, made a rare public appearance together Wednesday to discuss the American Masters episode, “Bing Crosby Rediscovered,” airing Dec. 2 on PBS.